Israel has instructed local authorities in the Golan Heights to “unlock and ready (bomb) shelters” after identifying what the military described on Tuesday as “irregular activity of Iranian forces in Syria”.

Israeli media said the order to prepare bomb shelters was unprecedented during Syria’s seven-year-old civil war, in which Israel is formally neutral.

In its statement, the IDF further said that its defense systems had been deployed “and IDF (Israel Defence Force) troops are on high alert for an attack, and any aggression against Israel will be met with a severe response.”

A number of reservists were also called up from the air defense, intelligence and Home Front Command units.

The IDF said it deployed missile defense batteries in northern Israel.

There was no immediate comment from Israel, which almost never confirms or denies airstrikes in Syria. Such strikes have become more frequent recently, amid soaring tensions between regional archenemies Israel and Iran.

Iran has vowed to retaliate to recent Israeli strikes in Syria targeting Iranian outposts in the country. They include an attack last month on Syria’s T4 air base in Homs province that killed seven Iranian military personnel, for which Tehran has vowed to retaliate. On April 30, Israel was said to have struck government outposts in northern Syria, killing more than a dozen pro-government fighters, many of them Iranians.

The IDF said it is prepared for “various scenarios” and warned “any aggression against Israel will be met with a severe response.”

Israel has warned it will not tolerate Tehran establishing itself militarily on its doorstep in Syria.